Correlation between circulating dendritic cell subsets and disease activity markers. Circulating plasmacytoid dendritic cell (pDC) and myeloid dendritic cell (mDC) counts (mean numbers/ml blood) from rheumatoid arthritis (RA) patients (n = 60) plotted against (a) Health Assessment Questionnaire (HAQ) score, (b) Disease Activity Score in 28 joints (DAS28), and (c) C-reactive protein (CRP) level. (d) The mDC level in synovial fluid (SF) of patients with active RA is significantly increased compared with that in osteoarthritis patients. Dendritic cell (DC) subsets were measured in the SF of patients with RA (n = 9) and in osteoarthritis patients (n = 11). The percentage of CD11c+CD123-HLADR+ mDCs and CD11c-CD123+HLADR+ pDCs in Lin- cells (CD3-, CD14-, CD16-, CD56-, CD8-, CD19-) are shown (mean ± standard deviation). **P < 0.001, Mann–Whitney U test. (e) The mDC:pDC ratio in SF from RA subjects is significantly increased compared with the ratio in matched peripheral blood (PB) samples. Squares and triangles indicate individual matched samples (n = 9). The ratio is calculated from the percentage of mDCs and pDCs in Lin- cells. ***P < 0.01, Mann–Whitney U test.